1. Field of the Invention
This invention relates generally to a printing system including thin film electroluminescent (TFEL) edge emitter structures for use as a high resolution light source and an electronic interface for use with the edge emitter structure of the printing system.
2. Background Information
It is known that an electroluminescent device generally, and particularly a thin film electroluminescent (TFEL) edge emitter device, may be utilized to provide an electronically controlled, high resolution light source. One thin film electroluminescent edge emitter structure has been proposed that includes a first dielectric layer disposed on a common or bottom electrode, a second dielectric layer spaced from the first dielectric layer, a phosphor layer interposed between the first and second dielectric layers and an excitation or top electrode disposed on the second dielectric layer. At least one of the electrodes, for example, the excitation or top electrode, is segmented to form a plurality of individual control electrodes in combination with the remaining structure to form a plurality of individual light emitting pixels.
It has also been proposed to use of TFEL edge emitters for electrophotographic printing. In one proposed system, input data is provided in serial form such that each line of data will activate selective consecutive pixels on a line across the TFEL a number of times per line of data. The process is then repeated many times to create a document. The application of electrical signals causes individual pixels to emit light energy at a light-emitting face. The light causes an image to be recorded on a photoreceptor upon which the emitted light strikes.
A TFEL edge emitter structure for multi-color light emission has also been proposed. This structure includes a common electrode layer, a phosphor layer, a dielectric layer, and control electrodes forming a stacked laminar arrangement and disposed on a layer of substrate material. An optical lens system receives radiated light energy from a plurality of light emitting pixels and forms a beam of light energy having a preselected, tightly controlled beam pattern. The multi-color light emission structure can be formed in a single TFEL edge emitter structure or formed as an array of separate TFEL edge emitter structures.
In applying a multi-color light emission TFEL edge emitter structure to a printing apparatus, a number of problems have arisen. For example, much greater accuracy in light levels is required in a color TFEL printing system as opposed to a black-and-white TFEL printing system in order to properly control the blending of the colors of light emitted by the edge emitter devices. In black-and-white systems, it is generally only necessary to provide enough light levels to replicate the gray scale levels that are distinguishable by the human eye. This level is approximately 64, depending somewhat on the resolution. The use of a similar number of light levels in a color TFEL edge emitter printing system, however, will cause the colors to blend in an improper manner resulting in an insufficient reproduction of the color desired to be printed. For color reproduction, three characteristics need to be controlled: hue, lightness (value), and chroma (level of color saturation). As a result, an electronic interface for receiving image data and supplying signals for driving a black-and-white TFEL edge emitter in a black-and-white printing system does not provide sufficient control for driving a multi-color TFEL edge emitter structure in a color printing system. Therefore, there is a need for a color printing system that can accurately respond to a sufficient number of light levels for each color in order to accurately reproduce shades of color on a printed document. There is also a need for an electronic interface for accepting serial image data from a computer within the printing system and driving the multi-color TFEL edge emitter structure that can provide the required light levels and accuracy for good quality color printing.
In addition, problems can occur in TFEL edge emitter devices due to the fact that all members of any large group of pixels in the prior art devices will not have identical output levels. In addition, the output level of a single pixel can change over time. Thus, the same signal applied to several pixels or applied to the same pixel at different times may result in different light outputs causing different light levels for the pixel produced therefrom. Although this nonuniformity is a problem in all TFEL edge emitter printing apparatus, it is particularly problematic in a color printing device because of the increased accuracy in light levels required for accurate reproduction of color shades. Therefore, there is also a need within a TFEL edge emitter printing system to allow the luminescence characteristics of each individual pixel or group of pixels to be adjusted both initially and later throughout the life of the system.